The present invention relates to paper structures having a decorative pattern, and more particularly to such a paper structure having regions of different basis weight arranged in a predetermined, nonrandom pattern.
Cellulosic fibrous structures, such as paper webs, are well known in the art. Such paper webs can be used for facial tissues, toilet tissue, paper towels, bibs, and napkins, each of which is in frequent use today. If these products are to perform their intended tasks and find wide acceptance, the fibrous structure should exhibit suitable properties in terms of absorbency, bulk, strength, and softness. Wet and Dry Tensile strengths are measures of the ability of a fibrous structure to retain its physical integrity during use. Absorbency is the property of the fibrous structure which allows it to retain contacted fluids. Both the absolute quantity of fluid and the rate at which the fibrous structure will absorb such fluid must be considered when evaluating one of the aforementioned consumer products. Further, such paper webs have been used in disposable absorbent articles such as sanitary napkins and diapers.
Attempts have been made in the art to provide paper having two different basis weights, or to otherwise rearrange fibers. Examples include U.S. Pat. No. 795,719 issued Jul. 25, 1905 to Motz; U.S. Pat. No. 3,025,585 issued Mar. 20, 1962 to Griswold; U.S. Pat. No. 3,034,180 issued May 15, 1962 to Greiner et al; U.S. Pat. No. 3,159,530 issued Dec. 1, 1964 to Heller et al; U.S. Pat. No. 3,549,742 issued Dec. 22, 1970 to Benz; and U.S. Pat. No. 3,322,617 issued May 30, 1967 to Osborne.
Separately, there is a desire to provide tissue products having both bulk and flexibility. Improved bulk and flexibility may be provided through bilaterally staggered compressed and uncompressed zones, as shown in U.S. Pat. No. 4,191,609 issued Mar. 4, 1980 to Trokhan, which patent is incorporated herein by reference.
Several attempts to provide an improved foraminous member for making such cellulosic fibrous structures are known, one of the most significant being illustrated in U.S. Pat. No. 4,514,345 issued Apr. 30, 1985 to Johnson et al., which patent is incorporated herein by reference.
Another approach to making tissue products more consumer preferred is to dry the paper structure to impart greater bulk, tensile strength, and burst strength to the tissue products. Examples of paper structures made in this manner are illustrated in U.S. Pat. No. 4,637,859 issued Jan. 20, 1987 to Trokhan, which patent is incorporated herein by reference. U.S. Pat. No. 4,637,859 shows discrete dome shaped protuberances dispersed throughout a continuous network, and is incorporated herein by reference. The continuous network can provide strength, while the relatively thicker domes can provide softness and absorbency.
One disadvantage of the papermaking method disclosed in U.S. Pat. No. 4,637,859 is that drying such a web can be relatively energy intensive and expensive, and typically involves the use of through air drying equipment. In addition, the papermaking method disclosed in U.S. Pat. No. 4,637,859 can be limited with respect to the speed at which the web can be finally dried on the Yankee dryer drum. This limitation is thought to be due, at least in part, to the pattern imparted to the web prior to transfer of the web to the Yankee drum. In particular, the discrete domes described in U.S. Pat. No. 4,637,859 may not be dried as efficiently on the Yankee surface as is the continuous network described in U.S. Pat. No. 4,637,859. Accordingly, for a given consistency level and basis weight, the speed at which the Yankee drum can be operated is limited.
Conventional tissue paper made by pressing a web with one or more press felts in a press nip can be made at relatively high speeds. The conventionally pressed paper, once dried, can then be embossed to pattern the web, and to increase the macro-caliper of the web. For example, embossed patterns formed in tissue paper products after the tissue paper products have been dried are common.
However, embossing processes typically impart a particular aesthetic appearance to the paper structure at the expense of other properties of the structure. In particular, embossing a dried paper web disrupts bonds between fibers in the cellulosic structure. This disruption occurs because the bonds are formed and set upon drying of the embryonic fibrous slurry. After drying the paper structure, moving fibers normal to the plane of the paper structure by embossing breaks fiber to fiber bonds. Breaking bonds results in reduced tensile strength of the dried paper web. In addition, embossing is typically done after creping of the dried paper web from the drying drum. Embossing after creping can disrupt the creping pattern imparted to the web. For instance, embossing can eliminate the creping pattern in some portions of the web by compacting or stretching the creping pattern. Such a result is undesirable because the creping pattern improves the softness and flexibility of the dried web.
PCT Publication WO 96/35018 discloses a paper sheet having a decorative pattern corresponding to areas having a translucent appearance corresponding to a relatively lower basis weight. It is believed that one problem associated with such paper is that tissue paper webs with translucent areas can be considered unfavorable by consumers. For instance, consumers can perceive such low basis weight regions as indicating weakness and/or lack of softness. Further, an excessive amount of low basis weight area can reduce the strength of the paper, making it unsuitable for the task the paper web is intended to perform.
Accordingly, it would be desirable to overcome such problems, and particularly to overcome such problems as they relate to a single lamina of paper. Specifically, it would be desirable to provide a non-through air dried paper web having a decorative pattern without compromising the strength, absorbency, and softness characteristics of the paper web. It would also be desirable to provide a paper web having a non-embossed decorative pattern without requiring translucent areas, as well as such a paper web having a multi-region background, as well as providing a method for forming such a paper web on a conventional, non-through air dry paper without the need for substantial modification of the papermaking machine.
The present invention provides a paper web having a first surface and an oppositely facing second surface. The paper web has a background portion and a non-embossed decorative pattern. The decorative pattern includes at least one high basis weight region having a basis weight which is greater than the average basis weight of the surrounding background portion.
The decorative pattern can comprise one or more low basis weight regions. The relatively low basis weight regions have a basis weight less than the average basis weight of the surrounding background portion, and the low basis weight regions can substantially circumscribe one or more high basis weight regions. At least some of the low basis weight regions can be disposed intermediate the background portion and the high basis weight regions, and at least some of the low basis weight regions can separate adjacent high basis weight regions. By substantially circumscribing one or more high basis weight regions, the low basis weight regions help to accentuate the visual appearance of the decorative indicia.
The term xe2x80x9cdecorative patternxe2x80x9d as used herein refers to a recognizable shape or shapes imparted to the web, preferably during initial formation of the web. Such shapes include, but are not limited to, floral shapes, animal shapes, geometric shapes, and the like.
The background portion preferably comprises at least 50 percent of the surface area of the first surface of the paper web, and in one embodiment the background portion comprises at least 70 percent of the first surface of the paper web.
In one embodiment, the decorative pattern can comprise less than about 500 decorative indicia per square foot of the web. The pattern can comprise between about 1 and about 300 discrete decorative indicia per square foot of the web, more preferably between about 1 and about 200 discrete decorative indicia per square foot, and even more preferably between about 10 and about 75 decorative indicia per square foot of the web.
The background portion can have an average basis weight of at least about 12 grams per square meter, and in one embodiment the background portion can have an average basis weight of at least about 15 grams per square meter. The decorative pattern can include at least one high basis weight region having a basis weight which is at least about 1.25 times the average basis weight of the surrounding background portion. The high basis weight regions of the decorative pattern preferably comprise less than 30 percent of the first surface of the paper web.
The background portion preferably has an opacity of at least about 2.8, and more preferably at least about 3.0. The opacity is measured using a procedure set forth below. At least a portion of the decorative pattern preferably has an opacity greater than the opacity of the background portion.
In one embodiment, the paper web has a total tensile strength of at least about 250 grams per inch, more preferably at least about 400 grams per inch; a machine direction elongation of at least about 8 percent, and a cross-machine direction elongation of at least about 4 percent, preferably at least about 6 percent. The paper web can have a dry burst strength of at least about 75 grams, preferably at least about 120 grams. In one embodiment, the ratio of the burst strength to the total tensile strength is at least about 0.3. Such a paper web provides the aesthetic benefits associated with a decorative pattern without sacrificing strength and elongation properties. The total tensile strength, elongation, and burst strength are measured using procedures set forth below.
The background portion preferably comprises at least two regions disposed in a nonrandom, repeating pattern and distinguishable from each other by at least one property, such as basis weight, density, or fiber composition. In one embodiment, the background portion comprises at least two regions distinguishable from each other by basis weight. Such a multiple basis weight background portion is believed to enhance the elongation properties of the web, and increase the ratio of burst strength to total tensile strength.
Two or more paper webs having a background portion and decorative pattern having at least one high basis weight region can be joined together to provide a multiple ply paper product.
The present invention also provides a method for making a paper web having a background portion and a decorative pattern which includes at least one high basis weight region. The method includes the steps of: providing a plurality of cellulosic fibers suspended in a liquid carrier, such as water; providing a fiber retentive forming element having liquid pervious zones; and depositing the cellulosic fibers and the liquid carrier onto the forming element. The method further includes the steps of draining the liquid carrier through the forming element in at least two simultaneous stages to form a web having a background portion and a decorative pattern which includes at least one high basis weight region having a basis weight greater than the average basis weight of the surrounding background portion.
The method can further include the steps of providing a web support apparatus having a web patterning surface; transferring the web from the forming element to the web patterning surface of the web support apparatus; and selectively densifying at least a portion of the web to provide a continuous network, high density region and discrete, relatively low density regions.